The present invention relates to micro surgical instruments, and in particular, to micro surgical instruments that are used in spinal surgery.
The use of this instrument is for microsurgery, as in an anterior cervical discectomy where one is removing the disc from between the cervical vertebrae. In a disc herniation, the disc may fragment and go out the back of the annulus (sequester) and yet remain superficial to the posterior longitudinal ligament, the ligament, which runs from vertebrae to vertebrae at the most posterior aspect of the bodies, or it may pierce the posterior longitudinal ligament and come to lie between the posterior longitudinal ligament and the dural sac containing the spinal cord.
Cutting in a downward motion on top of the dural sac containing the cerebrospinal fluid and spinal cord would be extremely dangerous. Even cutting the dural sac without damaging the spinal cord directly causes a very serious problem in that leak in this area is extremely difficult, if not impossible, to repair as there is no room available for suturing.
Therefore, at the present time, there is no easy way to get through the tissues of the posterior longitudinal ligament, or for that matter the posterior annulus when going after sequestered disc fragments. The current state of the art is to use either a micro hook which is nothing more than a button hook type device on a very small scale of one to two millimeters, which is then used to slowly pick away at the fibers of the posterior longitudinal ligament, which is a tedious task. One then uses the small hook to fish blindly behind the ligament for the suspected disc fragment. As the area behind the posterior longitudinal ligament is not visualized one can never be certain as to whether any disc material is there to begin with or still remains. This may result in wasted time on the one hand, or inadequate removal with a poor result on the other.
An alternative method used, at the present time is to take a kerrisson rongeur which is a rongeur which cuts with an up and down motion and to try to put the foot of the rongeur deep to the posterior annulus and posterior longitudinal ligament and then to cut what is between the jaws. There are at least two problems associated with this. The first is that the deep portion of the jaw is in a blind area so that one can not be sure what else is being cut and secondly, frequently there is a tearing rather than a cutting of the tissue. The fact that one is working through a deep and narrow opening limits significantly the available options for removing this tissue. A blade which cuts by safely passing beneath tissue and cutting only on its upper visible surface is a dramatic improvement from the current state; and would be of great value in other applications of microsurgery such as intracranial neurosurgery.